1. Field of the Invention
The present invention relates to a seat cushion structure for use in a seat in a vehicle, particularly an automobile.
2. Description of the Prior Art
One known seat cushion structure for use a vehicle seat is illustrated in FIG. 1 of the accompanying drawings. The known seat cushion structure is composed of a plurality of cushion springs 22 extending below and along the lower surface of a cushion foam body 21 of a seat bottom unit 20 and resiliently supporting the cushion foam body 21, a seat cushion frame 23 supporting the cushion springs 22, and a border wire 24 mounted on the seat cushion frame 23 and supporting lateral side portions 21a (only one shown in FIG. 1) of the cushion foam body 21.
Fishmouth springs 25a, 25b are coupled between front and rear ends 22a, 22b of each of the cushion springs 22 and the seat cushion frame 23 to resiliently support the front and rear ends 22a, 22b of the cushion spring 22. The border wire 24 is resiliently supported by formed springy wires 26 (one shown) connected between the border wire 24 and the seat cushion frame 23.
The knees of the seat occupant can be supported by the fishmouth springs 25a coupled to the front ends 22a of the cushion springs 22, and the thighs of the seat occupant can be supported by the fishmouth springs 25b coupled to the rear ends 22b of the cushion springs 25b. The formed wires 26 connected to the border wires 24 are effective in supporting sides of the occupant's thighs.
With the above prior seat cushion structure, as described above, the fishmouth springs 25a, 25b are attached to the front and rear ends of the cushion springs 22 and the formed wires 26 are attached to the border wire 24 for supporting the knees, thighs, and thigh sides of the seat occupant. The fishmouth springs 25a, 25b and the formed wires 26 are complex in shape unlike so-called S-shaped springs such as the cushion springs 22, and hence are expensive. Therefore, the conventional seat cushion structure as a whole has been costly to manufacture.
Seat cushion frames support cushion springs disposed below a seat cushion foam body and resiliently supporting the cushion foam body. The cushion foam body is covered with a cover material having edges fastened to the seat cushion frame. As disclosed in Japanese Patent Publication No. 55-14646, the seat cushion frame comprises a rectangular frame body with the cushion springs extending beween and secured to front and rear edges of the frame body. The cover has its entire peripheral edge fastenable to the seat cushion frame. The seat cushion frame can support the seat cushion foam body as a whole.
The seat cushion frame is generally be formed by pressing a metal sheet. Since the front and rear edges of the seat cushion frame support the cushion springs, they are subjected to a high load imposed by the seat occupant through the cushion springs. To give the front and rear edges of the seat cushion frame a sufficient mechanical strength, the seat cushion frame has been formed by deep-drawing the metal sheet. The production of such seat cushion frames however results in a poor material efficiency. The deep-drawing process requires a number of pressing steps, with the result that the seat cushion frame is expensive to manufacture.